Planets

Pluto and its moons

Pluto is now known to have at least five moons, which David Tholen and his colleagues have been studying using the Hubble Space Telescope.

They have concluded that the orbit of Charon is circular to within 3 km, as expected from tidal dissipation effects. and that threeof the outer satellites have orbits close to the 4:1 (Nix), 5:1 (P4), and 6:1 (Hydra) resonances with Charon .

The orbits are also being used to plan the observational sequence for the New Horizons spacecraft when it flies through the Pluto system in July 2015.

Pluto and its moons: the outer satellites are circled. Pluto and Charon are saturated.

Planetary Atmospheres

Toby Owen studies the origin of planetary atmospheres by comparing the abundances and isotope ratios of noble gases and abundant elements in different solar system objects. These studies are based primarily on data obtained from instruments flown on deep space missions to planets and comets.

Data he obtained from the mass spectrometer on the Viking Mars lander suggested a striking similarity between components of the atmospheres of Mars and Earth. The Mars Rover Curiosity, which recently landed on the surface of Mars carries both infrared and mass spectrometers that will repeat and extend the Viking measurements with much higher precision. This will enable a rigorous comparison of Mars with Earth. If the new direct measurements on Mars duplicate the terrestrial array of noble gases, a common source (comets perhaps?) for some fraction of the volatiles on these planets is implicated.

Owen is also participating in the Juno mission to Jupiter to measure the abundance of water, and hence oxygen.